Oronasal delivery of drugs has long been known and has gained wide acceptance. Pharmaceuticals for the treatment of tracheal, bronchial, nasal and pulmonary conditions are widely available in prescribed or metered doses in small pressurized aerosol canisters. While medications can be dispensed directly from such canisters into the oronasal passages of patients, experience has proven that patients generally have not made optimum use of and/or have not obtained optimum benefits from medications delivered directly from the aerosol canisters.
Because direct use of the aerosol canisters has not proven effective or efficient for a large proportion of patients, many devices have been proposed for converting the medications from the concentrated pressurized form in which they are discharged from aerosol canisters into a nonpressurized and less concentrated form in order to be more readily and efficaciously inhaled by the patient. Further, it has been found that a long and slow inspiration of the medication promotes a highly efficient distribution of medication to partially occluded airways. Thus, it is desirable in such devices to inhibit rapid inhalation and to encourage a long and slow inspiration period.
In order to promote a long and slow inspiration period, it is desirable to provide an expandable breathing bag or spacer, so that the patient is required during respiratory maneuvers to utilize a negative thoracic pressure upon inhalation, thereby to inhibit rapid inhalation and encourage long and slow inhalation. Representative prior art devices having expandable and contractible breathing bags or spacer chambers may be found by way of example, in U.S. Pat. No. 4,938,210 to Shene, U.S. Pat. No. 4,940,051 to Lankinen, U.S. Pat. No. 5,040,527 to Larson et al., U.S. Pat. No. 4,484,577 to Sackner et al., and U.S. Pat. No. 5,318,016 to Mecikalski.